The present invention relates to a noise reducing apparatus for reducing noise in moving images using the field or frame correlation of video signals of televisions, videos, and video cameras. In this case, the noise may be effectively reduced without causing residual images or the like on the output images even when inputting images having fast movement, and when inputting images having slow movement, by controlling the apparatus using a movement detecting circuit when a changing operation is often effected in the movement of the inputted picture signals. More particularly, the present invention relates to a noise reducing apparatus for effecting the best noise reducing operation with respect to the noise produced in edge portions by the movement of the inputted images by the provision of an optimum value of a nonlinear processing method used in this system.
FIG. 13 is a block diagram showing a conventional noise reducing apparatus.
An input video signal is converted into a digital signal by an A/D converter 2 when the video signal is inputted from the inputting terminal 1. The digital signal subtracted therefrom by has a non-correlated component to be described later passing it through a subtracter 3. The digital signal becomes a picture signal component which ideally does not contain the noise component, and is stored in a frame memory 4, and is delayed by one frame period. Since the picture signal delayed by one frame portion is inverted from one frame signal with respect to the phase of the color signal, it is phase compensated by a color signal phase shifting circuit 5. Only the phase of the color signal is inverted. Thereafter, a difference signal (frame difference signal) of the two picture signals which are equal in chroma phase is obtained by the subtracter 6. The frame difference signal is converted into a parallel digital signal from a serial digital signal by a serial - parallel converter 7. The frame difference signal is divided into the frequency component by a Hadamard transform converting circuit 8. Only the noise component of a small level can be taken out from each of these components through a nonlinear processing circuit 9. The respective components extracted by the nonlinear processing circuit 9 are returned by passing the signal through a the Hadamard transform inverse inverting circuit 10 to the original time axis, where the parallel digital noise signal may be obtained. In a parallel - serial converting circuit 11, the parallel digital noise signal is turned into a serial signal which is similar to the input form. The signal obtained here is a noise component signal extracted only from the frame difference signal which does not have the frame correlation. It is fed into the subtracting circuit 3 as described hereinabove. A digital picture signal free from noise is obtained by the subtracting of the noise components from the input picture signal. Finally, the digital picture signal is converted into the original analog signal and is outputted by the A/D converter 12.
Such an apparatus as described hereinabove has a problem in that the residual images are caused with respect to the moving amount of the input images when the level of the nonlinear circuit is raised so as to improve the S/N improvement degree with the input images being the moving images.
Although the S/N improvement effect and the residual image characteristic of the edge portion visually becomes very different due to the nonlinear processing, the optical characteristics of the nonlinear characteristics are not proposed.